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• The UF researchers have identified citrus cultivars, in this case 16 citrus rootstocks, most of which show a lower rate of infection and more tolerance to citrus greening.

SHOWN HERE is a grapefruit rootstock trial with trees infected with citrus greening that is being studied by University of Florida Institute of Food and Agricultural Sciences researchers with the UF/IFAS Citrus Research and Education Center in Lake Alfred. The tree in the foreground, although infected with citrus greening, is healthy in appearance, while the trees next to it are also infected but are in poor shape.

University of Florida researchers have found encouraging results in the ongoing battle against citrus greening disease.

The UF researchers have identified citrus cultivars, in this case 16 citrus rootstocks, most of which show a lower rate of infection and more tolerance to citrus greening — the dreaded disease that has devastated Florida’s citrus industry since its arrival in 2005.

Growers use citrus rootstocks, part of a plant that includes a portion of root, as a foundation to graft new trees, as opposed to growing them from seed.

For now, data on the rootstocks are limited, but the scientists will gauge their potential in test plots, and UF fast-tracked their release this summer for large-scale testing by an industry in dire need of solutions.

Greening has cost Florida’s economy an estimated $4.5 billion in lost revenues since 2006 and poses a huge threat to the state’s $9 billion citrus industry, the nation’s largest. It weakens and eventually kills infected trees.

Greening has also spread to the country’s other big citrus-producing state, California, where it was detected in 2012.

Large-scale trials of the promising rootstocks could begin in March 2014, and it could be another three to five years before they are available to growers, said Jude Grosser, a horticulture professor with UF’s Citrus Research and Education Center in Lake Alfred.

Grosser and Lake Alfred colleagues Fred Gmitter, a horticulture professor, and Bill Castle, a horticulture professor emeritus, have led the effort to develop the rootstocks. They are all faculty members in UF’s Institute of Food and Agricultural Sciences.

“What’s happening is fields are becoming living laboratories now because the greening disease is spreading so quickly,” Grosser said. “Some people have estimated that 70 percent of the trees in the entire state are infected now, and it’s predicted to go up in the 90s in a very short time.”